Kore has designed a number of high-precision sample stages for operation in UHV environments. For matching the cryo preparation system, we have designed an X, Y, Z stage with ± 12 mm of motion in all directions. The stage fits on to a 8″ flange and is designed to maintain samples cold for surface analysis of otherwise volatile materials.
Using on-stub thermometry and control of the LN2 flow, the sample can be held at any temperature from -180°C to room temperature to within ± 1°C. The X, Y and Z motions are achieved through manual, rotary motion, and an option exists to equip the drives with digital micrometer readouts for greater positioning precision.
A pneumatic actuator is used to clamp the sample in the holder providing a substantial contact force between the cold reservoir and the sample block. This method ensures very good thermal contact and minimal temperature difference between the liquid nitrogen cooled reservoir and the specimen block. The clamp is fully UHV compatible and is released by the transfer rod before the specimen is unloaded from the stage.
|Active LN2-cooled sample block||Permits analysis of otherwise volatile materials in a vacuum|
|2 separate cooling circuits||Permits a cold plate near the sample to be held at lower temperature than sample|
|On-stub thermometry||Precise temperature measurement|
|Very stiff mechanical design||Permits high resolution imaging (minimise drift during data acquisition)|
|X, Y, Z motion stage: ±12mm on all axes||Full analytical coverage of the 22mm x 22mm sample stub|
|Pneumatic sample clamp||Ensures good thermal contact (<80(K on stub). Released for easy sample exchange|
|Option for digital micrometer readouts||Precision positioning|
In order to cool the stage down to LN2 temperatures Kore uses a method that has proven superior in practice to simply pumping LN2 through the cooling pipes within the cold stage. The problem with this latter method is that it is almost impossible to prevent moisture getting into a typical vessel, and after some time ice formation within the narrow bore supply-pipes causes flow restriction and poor cold stage performance. Instead, Kore flows pure nitrogen gas through a condenser coil within the Dewar, and thus the cold reservoir and the coolant gas are de-coupled. This maintains unobstructed lines within the supply pipes.
A 20-25 litre Dewar is used to supply LN2 for the experiments. In practice we have seen a consumption of ~10 litres during a full day’s experiments, and thus the 20-25 litre Dewar is appropriate. Sitting on top of the Dewar is a manifold system comprising a by-pass valve to allow maximum initial flow for fast cooling, plus a separate line with a flow controller. The client supplies nitrogen gas into the manifold system. Insulated lines take the cold gas in and out of the stage. Once the stage has cooled to near the operating temperature, the by-pass line is closed and the flow is controlled thereafter with the controller. After some initial set-up trials, it is possible to use the same setting of the flow controller to achieve a standard temperature at the sample stub.
The sample stub has an onboard thermocouple, and the temperature on-stub is monitored using a separate, free-standing, LCD readout temperature unit which is also supplied as part of this kit (mains powered and fitted into a tilted desk case). Please note that the temperature measurement can only be performed when the sample stage potential is off, and the thermocouple plug must be removed to re-attach the stage potential prior to performing SIMS.
Kore Technology is a centre of excellence in time-of-flight mass spectrometer technology and has a very strong R&D capability in terms of its personnel, all of whom have been heavily involved in a variety of analytical instrumentation development programmes.